This invention relates to a pressure control device for use in a dual hydraulic braking system of a vehicle such as an automobile, and more particularly, to improvements in a pressure control device which controls liquid pressures prevailing in two separate circuits so as to maintain a predetermined ratio therebetween and issues a warning signal when there occurs a difference over a given value range between both pressures.
It is a common practice to use a brake utilizing liquid pressure in a vehicle such as an automobile, because of its superiority in smoothness and reliability in operation. However, such a liquid pressure type brake suffers from a danger that, if a liquid leakage occurs, the brake will entirely cease to function. Thus, there has been widely used the so-called dual system, in which two independent braking circuits apply liquid pressure to the respective wheel cylinders.
Among those dual braking systems, there is known such a system which issues a warning signal such as by means of a lamp or a buzzer when the difference in the liquid pressure between both circuits exceeds a predetermined value. In a prior art braking system of the type described, the warning device will be actuated to issue a warning signal when the brake is applied and the difference in braking pressure between two circuits is above a predetermined value, but, if the brake is released, then the warning signal will no longer issue. Apart from this, there is known a system which issues a warning signal when there occurs a difference in liquid pressure between two circuits, and yet continues to issue the signal even after the brake has been released.
However, such warning devices are not adapted for use in a dual braking system in which braking pressures in two circuits are different to each other.
Further, it is also known and important to attain a balance in pressure between both circuits in applying the brake so that even and simultaneous braking forces are afforded to wheels on both sides of the vehicle, thus, there should be provided a device for eliminating small variations in braking pressure between both circuits.